Production of bonded nonwovens by the wet method

ABSTRACT

Bonded nonwovens can be produced with particular advantage by the wet method by treating the textile fibers prior to the addition of the binder polymers with water-soluble cationic polycondensation products which have been prepared from carbamides, formaldehyde, dicyanodiamide and salts of ammonia or of amines.

, Etc

States i atent Stephan et al. [4 1 Jan. 18, 1972 PRODUCTION OF BONDED 6]References Cited .NONWOVENS BY THE WET METHOD UNHED STATES PATENTS [721Invenwm z Ludwigshafen; ""F 2,927,051 3/1960 Buckwalter et al. ..l56/314x well, Mannhem; Hans 3,510,390 5/1970 Bjorksten eta] ..156/314 xburgerhof; Hans-Ulrich Frank, Ludwlgshafen an of Germany PrimaryExaminer-Carl D. Quarforth 7 Assignee; Badische m & SUdaJabI-ik m 1Assistant Examiner-Stephen J. Lechert, Jr. geseuschafl,Ludwigshafenfkhine; Attorney-Johnston, Root, OKeefie, Keil, Thompson &Shur- "515,15, tleff [22 Filed: June 27, 1969 J [57] ABSTRACT PP 9Bonded nonwovens can be produced with particular advantage by the wetmethod by treating the textile fibers prior I to the addition of thebinder polymers with water-soluble ca- [301 Application Priority Datationic polycondensation products which have been prepared June 29, 1968Germany ..P 17 69 700.6 from carbamides, formaldehyde, dicyanodiamideand salts of ammonia or of amines. [52] US. Cl..l56/315,156/181,156/331,

156/332, 156/333, 156/334 8 Claims, No Drawings [51] Int. Cl. C09j 5/04[58] FleldoiSearch ..156/l81,281,314,331,315,

PRODUCTION OF BONDED NONWOVENS BY THE WET METHOD This invention relatesto a process for the production of bonded nonwovens by the wet method.

In the wet method for the production of bonded nonwovens natural orsynthetic textile fibers are suspended in an aqueous medium and abonding agent is added. The aqueous medium is then separated on amachine substantially resembling known paper machines and the resultantweb is generally dried at elevated temperature.

Fibers known as binder fibers, for example of polyvinyl acetate or ofcellulose loaded with polyacrylates, are often used as binders forbonding nonwovens. The webs of fibrous material thus acquire adequatewet tear resistance to enable them to be removed from the wire of themachine. When drying and heating is carried out, the polyvinyl acetatefibers or the polyacrylates are softened so that the textile fibers arebonded together. The tear resistance of bonded nonwovens obtained bythese known methods is however inadequate. For this reason, the bondednonwovens are often additionally impregnated with a plastics dispersionor solution. However, the handle of nonwovens prepared in this way isusually hard and similar to that of paper.

It is furthermore known from British Pat. No. 1,071,]36 that paper andnonwovens can be prepared from fibers which have been treatedsuccessively with melamine resins or urea resins and an aqueousdispersion of a plasticized thermoplastic. If bonded nonwovens areprepared from such pretreated plastics by the wet method, products areobtained however from which the plasticizer can easily migrate. As aresult, the handle becomes less good and in some cases the materialbecomes more prone to soiling.

The object of the present invention is an improvement in the knownmethod for the production of bonded nonwovens by the wet process inwhich conventional binder polymers can be used and in which nonwovenshaving particularly high initial tear resistance and particularly hightensile strength are obtained- We have now found that the production ofbonded nonwovens by the wet method bysuspending textile fibers in anaqueous medium, precipitating a binder polymer dispersed in the aqueousmedium ontothe fibers, separating the aqueous medium and drying thenonwoven at elevated temperature, can be advantageously carried out bytreating the textile fibers with water-soluble cationic polycondensationproducts which have been prepared from a carbamide, formaldehyde,dicyandiamide and a salt of ammonia or of an amine.

Suitable water-soluble cationic polycondensation products of acarbamide, formaldehyde, dicyandiamide and a salt of ammonia or an amineare obtainable for example according to the process of German Pat. No.1,078,768 according to which condensation products having a uniformdegree of condensation from formaldehyde and a carbamide such as urea,alkylureas, acetylenediurea with dicyandiamide and with a salt ofammonia or an aliphatic amine are condensed with an inorganic or strongorganic acid and if desired with a further amount of formaldehyde;hexarnethylene tetramine may also be cocondensed. Instead of usingcondensation products having a uniform degree of condensation fromformaldehyde with carbamides, similar products having a nonuniformdegree of condensation may be used.

Examples of particularly suitable alkylureas for the production of thecationic polycondensation products are N-alkylureas andN,N'-dialkylureas whose alkyl groups usually have one to three carbonatoms, such as N-methylurea, N,N'- dimethylurea, N-ethylurea,N,N'-diethylurea, N-n-propylurea and N,N'-diisopropylurea. Alkylureas ofthe said type which containmore than three, for example from four tosix, carbon atoms in their alkyl groups are also suitable. Suitablecarbamides of the said type generally contain one to seven, preferablyone to four, carbon atoms and urea is the preferred carbamide. Suitablealiphatic amines for formation of salts are particularlyN-monoalkyl-amines, N,N-dialkylamines, N-al-' kylolamines,N,N-dialkylolami esand N,N,N-trialkylolamines whose alkyl radicalsusually contain from one to three, particularly one or two, carbonatoms. Specific examples are methylamine, ethylamine, propylamine,isopropylamine, dimethylamine, diethylamine, ethanolamine, N,N-diethanolamine and triethanolamine. Examples of salts of ammonia areammonium chloride, bromide, phosphate, formate and chloroacetate.

In the production of the condensation products by condensation inalkaline or acid medium for example according to the method known fromGerman Pat. No. 1,078,768, generally from two to four moles offormaldehyde are used for each mole of carbamide of the said type in thefirst stage.

Low molecular weight compounds can be used as starting material for thesecond stage of the process. These may be (when urea has been condensedwith formaldehyde) compounds such as dimethylolurea, trimethylolurea andtetramethylolurea. Higher molecular weight products which are stillsoluble in water and which have been obtained by further condensationmay however also be used. Condensation products which are already waterrepellent and which have been obtained by condensation at pH values ofless than 7.0 are also suitable.

Conversion of the neutral condensation products of the first stage intocationic products with dicyandiamide, ammonium salts or amine salts withor without an additional amount of formaldehyde may be carried out byseveral methods. For example the components of the second stage may beadded immediately to the reaction mixture of the first stage. Thereaction mixture of the first stage may be concentrated, for example byvacuum evaporation, prior to further processing. Condensation in thesecond stage is carried out in the acid range. The condensationtemperature may be from 50 to C.; the reaction period may be from 15minutes to 2 hours or more. Cationic condensation products having adefinite degree of condensation may easily be obtained in a reproduciblemanner by selection of the appropriate reaction conditions; the degreeof condensation may be regulated by reference to the viscosity or theturbidity point (cf. example 2) or the pH value.

As regards the amounts of the reaction components the following may besaid: calculated on a condensation product of the first stage obtainedfrom 1 mole of carbamide, particularly urea, about 0.5 to 2 moles ofdicyandiamide, l to 3 moles of ammonium or amine salt or a mixture ofsuch salts and in both stages together from 3 to 6 moles of formaldehydemay be used. The formaldehyde may be used in the form of the commercialaqueous solution of 30 by weight or 40 by volume strength; it mayhowever also be added as parafonnaldehyde to the aqueous solution of thecarbamide.

When using ammonium or amine salts of hydrochloric acid, products areobtained which are soluble in water in all proportions provided that atleast as many moles of formaldehyde have been cocondensed as there aremoles of carbamide, dicyandiamine and ammonium or amine salt present. 0nthe other hand sulfates or, generally speaking, anions having a greaterion radius give condensation products having a limited solubility inwater.

The solubility in water of products which are not dilutable in everyratio with water or the stability of condensation products which arecompletely soluble in water to precipitants, for example nitrate orsulfate ions, can be increased by introducing by condensation in the.second process stage about one-sixth to one-third of a mole ofhexamethylenetetramine. This additional measure is of special advantagewhen ammonium salts having anions of great radius, such as NO;,, 501"and I have been used in the condensation, because the water-solubilityof such condensation products is generally less than that of productsobtained under otherwise the same conditions with for example ammoniumchloride and ammonium bromide. When more than I mole of formaldehyde isused in the first stage of the condensation per mole of carbamide andthe moles of dicyandiamide and ammonium or amine salt to be "added tothe second stage, the excess moles of formaldehyde can be reacted byadding an appropriate amount of ammonia to form hexamethylenetetramineand the addition of hexamethylene tetramine can be dispensed with.

Polymers suitable for the preparation of bonded non- Wovens, which aregenerally in the form of their aqueous dispersions, are suitable asbinder polymers. Aqueous dispersions which contain from 40 to 60 percentby weight of acrylic ester and/or methacrylic ester polymers havingcarboxyl groups are particularly suitable. These polyacrylates areusually derived from esters of acrylic or methacrylic acid with alkanolscontaining from one to 12, particularly from one to eight, carbon atoms,which often form the major component of the copolymers. Suchpolyacrylates generally contain (as monomers having carboxyl groups)from 1 to percent by weight of polymerized units of a, B-olefinicallyunsaturated monocarboxylic and/or dicarboxylic acids which preferablycontain from three to five carbon atoms. The proportion of sucholefinically unsaturated carboxylic acids in the copolymers ispreferably from 2 to 2 percent by weight with reference to thecopolymer. Acrylic and methacrylic acid are particularly suitable;crotonic acid, maleic acid, fumaric acid and itaconic acid are alsosuitable. The polyacrylates may additionally contain polymerized unitsof further olefinically unsaturated monomers, for example vinyl-aromaticcompounds, such as styrene, vinyl halides or vinylidene halides, such asvinyl chloride and vinylidene chloride, acrylonitrile, methacrylonitrileand/or vinyl esters of saturated carboxylic acids containing from two to18, particularly two to three, carbon atoms, particularly vinyl acetateand vinyl propionate but also vinyl laurate, vinyl stearate and vinylpivalate, and also (usually in amounts of from 1 to 10 percent,particularly from 2 to 7 percent, by weight with reference of thecopolymer) of amides of a, Bolefinically unsaturated monocarboxylicand/or dicarboxylic acids usually containing from three to five carbonatoms or their derivatives, particularly acrylamide, methacrylamide,N-methylolacrylamide, N-methylolmethacrylamide,N-methoxymethylmethacrylamidc, N-n butoxymethylmethacrylamide,N-acetoxymethylacrylamide and N-acetoxymethylmethacrylamide, andvinyl-sulfonic acids or their salts. The aqueous dispersions of suchpolyacrylates may contain conventional anionic and/or nonionicemulsifiers with or without small amounts of protective colloids.

Other suitable binder polymers are the aqueousdispersions(conventionally used for the purpose) based on polymers of vinylchloride and/or vinylidene chloride, based on butadienestyrenecopolymers or butadiene-acrylonitrile copolymers and/or based on vinylester polymers, for example polymers of vinyl acetate or vinylpropionate, which may contain conventional anionic or nonionicemulsifiers with or without protective colloids. I

Generally from 1 to 10 percent, preferably from 3 to 6 percent, byweight of water-soluble cationic polycondensation products and from 10to 60 percent, preferably from 30 to 50 percent, by weight of binderpolymer (in each case calculated as solids and with reference to theamount of textile fibers) are used in the new process.

The amount of textile fibers (with reference to the amount of water) isusually from 0.5 to 3 percent, preferably from 0.7 to 1.5 percent, byweight, the fibers preferably having a length of from 5 to 30 mm. Thetextile fibers may consist for example of cellulose or cellulosederivatives, synthetic polyamides such as polycaprolactam orpolyhexamethylene adipamide, saturated polyesters such as polyethyleneglycol terephthalate, or polyacrylonitn'le.

1n the new process the synthetic fibers may be pretreated with thewater-soluble cationic polycondensation products in aqueous suspensionand used in the process according to this invention, if desired afterdrying. The pretreated fibers are then suspended in the aqueous mediumand then an aqueous dispersion of the binder polymer is added, generallywhile stirring. When the binder polymer has been precipitated onto thefibers, the material can be fed to the wire section of a webformingmachine, for example an inclined-wire machine, and

processed by suction or pressing in the conventional manner. The fibersloaded with the binder polymer are generally arranged as a thin sheetmaterial during separation of the aqueous medium. The web can then belifted off from the wire in the conventional way and dried at elevatedtemperature which is usually from 60 to 150 C., preferably from to 130C.

According to an advantageous embodiment of the process, a suspension ofthe textile fibers may have added to it first an aqueous usually from 5to 15 percent and preferably from 8 to 12 percent solution of thecationic polycondensation product and simultaneously or some minuteslater an aqueous dispersion of the binder polymer. Separation of theaqueous medium and drying of the web may be carried out in theconventional manner.

It is advantageous in the new process to add a resin soap to the aqueoussuspension of textile fibers in addition to the water-solublepolycondensation product and the binder polymer.

The new process gives bonded nonwovens which as compared with othernonwovens prepared by the wet method are distinguished by particularlygreat initial tear resistance, particularly high tensile strength and bya soft textile handle.

Additives conventionally used for finishing textiles and/or paper may beused in the conventional ways and if desired added to the aqueous mediumin the new process, provided they are compatible with the otheradditives.

The invention is illustrated by the following examples, in which partsand percentages are by weight.

EXAMPLE 1 Twenty-five kilograms of a mixture of polycaprolactam fibersof which half have a length of 8 mm. and the other half have a length of12 mm. is suspended in 2.5 m. of water with an addition of 250 g. of anoxyethylated fatty alcohol. While stirring, a solution of 1,500 g. of awater-soluble cationic polycondensation product prepared as described inexample 1 of Gennan Pat No. 1,078,768 from 1 mole of urea, 1 mole ofdicyandiamide, 3 moles of formaldehyde and 1 mole of ammonium chloridein 5 liters of water, and a solution of 250 g. or resin soap in 2.25liters of water and 20.5 kg. of a 50 percent aqueous dispersion of acopolymer of 93 parts of n-butyl acrylate, 1 part of acrylic acid, 3parts of N-methylolmethacrylamide and 3 parts of acrylonitrile areadded. The whole is stirred for another 10 to 20 minutes and the aqueoussuspension is introduced into a web-forming machine. The water isseparated and the web is lifted off and dried at 120 C. A nonwoven isobtained which in the dry condition has a tensile strength of 120kg./cm. measured according to DIN 53,1 12. The nonwoven has a softtextile handle and is suitable for the production of nonwoven clothing,disposable articles, disposable bed linen and the like.

Twenty kilograms of a mixture of equal parts of cotton linters and woolflock may be used instead of the polycaprolactam fibers.

EXAMPLE 2 Twenty-five kilograms of a mixture of equal parts ofpolycaprolactam fibers (1.5 denier/ 10 mm.), viscose rayon fibers (1.5denier/ 10 mm.) and beech sulfite cellulose is suspended in 2.5 m. ofwater. A solution of 2,000 g. of the water-soluble cationicpolycondensation product specified in example 1 in 10 liters of water isadded while stirring. It is allowed to go onto the fibers for 10 to 15minutes. Then a mixture of a solution of 750 g. resin soap in 10 litersof water and 22.5 kg. of a 50 percent aqueous dispersion of a copolymerof 93 parts of n-butyl acrylate, 1 part of acrylic acid, 3 parts of N-methylolmethacrylamide and 3 parts of acrylonitrile is added to thesuspension of fibers. After 10 to 20 minutes, the aqueous suspension ofthe fibers loaded with plastic is introduced into the web-formingmachine. The water is separated and the web is lifted off from the wireand dried at 120 C. A nonwoven is obtained which in the dry conditionhas a tensile strength of kg./cm. measured according to DlN 53,1 12.

The nonwoven has a soft textile handle and is suitable for theproduction of nonwoven clothing, furnishings, disposable articles andthe like.

' We claim:

1. In a wet method for production of nonwoven textile fiber articles bysuspending textile fibers in aqueous medium, depositing on the fibers abinder polymer dispersed in the aqueous medium, separating the aqueousmedium from the fibers loaded with the binder polymer and drying theresultant web at elevated temperature, the improvement which comprisestreating the textile fibers, prior to the addition of the binderpolymer, with a water-soluble cationic polycondensation product, whichhas been prepared from a carbamide containing from one to seven carbonatoms, formaldehyde, dicyandiamide and a salt of ammonia or an amine,said water soluble cationic polycondensation product having beenproduced by reacting (a) a water soluble condensation product offormaldehyde and said carbamide in a mole ratio or 1.2 to 4,respectively with (b) 0.5 to 2 moles of dicyanamide, and (c) at leastone of (a) l to 3 moles of an N-monoalkyl amine, an N,N-dialkylamine, anN-alkylolamine, an N,N- dialkylolamine or an N,N,N-trialkylolaminewherein the alkyl or alkylol groups thereof contain one to three carbonatoms or (b') l to 3 moles of an ammonium salt at 50100 C., in acidicaqueous medium, said moles being based upon 1 mole of said carbamide insaid water soluble condensation product, and the total moles offormaldehyde used in the preparation of said cationic polycondensationproduct being in the range of 3 to 6 moles per 1 mole of said carbamidein said condensation product (a).

2. In a method as claimed in claim 1, said carbamide having one to fourcarbon atoms.

3. In a method as claimed in claim 1, said carbamide being urea.

4. In a method as claimed in claim 1, said carbamide being urea,N-alkylurea or N,N-dialkylurea, said alkyl groups having one to sixcarbon atoms.

5. In a method as claimed in claim 1, said water soluble condensationproduct (a) being dimethylolurea, trimethylolurea or tetramethylolurea6. In a method as claimed in claim 1, the anions of said salts beingchloride, bromide, iodide, phosphate, fonnate, chloroacetate, sulfate ornitrate.

7. In a method as claimed in claim 1, and reacting with (a) and (b)about one-sixth to one-third mole of hexamethylenetetrarnine.

8. In a method as claimed in claim I, wherein the amount of said watersoluble cationic polycondensation product is l-lO percent by weight, ona solid basis, of said textile fibers.

7 3 3 3 I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo 3, 55,77 Da'ted January 18,1972

Inventofls.) Rudolf Stephan et a1 It is certified that error appears" inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2, line #8, "30 by weight or 40" should read 30% by weight or 40%I Column line 41, or should read of Column 5, line 19, "or" should readof Signed and sealed this 6th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTI'SGHALK I Attesting OfficerCommissioner of Patents

2. In a method as claimed in claim 1, said carbamide having one to fourcarbon atoms.
 3. In a method as claimed in claim 1, said carbamide beingurea.
 4. In a method as claimed in claim 1, said carbamide being urea,N-alkylurea or N,N-dialkylurea, said alkyl groups having one to sixcarbon atoms.
 5. In a method as claimed in claim 1, said water solublecondensation product (a) being dimethylolurea, trimethylolurea ortetramethylolurea
 6. In a method as claimed in claim 1, the anions ofsaid salts being chloride, bromide, iodide, phosphate, formate,chloroacetate, sulfate or nitrate.
 7. In a method as claimed in claim 1,and reacting with (a) and (b) about one-sixth to one-third mole ofhexamethylenetetramine.
 8. In a method as claimed in claim 1, whereinthe amount of said water soluble cationic polycondensation product is 1-10 percent by weight, on a solid basis, of said textile fibers.